Fix visuals of tutorial notebooks

[Mr-Geekman]

🚀 Feature Request

There are some problems with visual representation of the tutorial notebooks in the documentation, we should fix them and unify the style of notebooks.

Proposal

Problems in tutorials:

• Poor representation of dataframes: bad alignment, it was better in the old version of documentation
• Not working table of contents
  • It isn't critical because TOC is displayed on the right panel of the web-site
• Not working binder button
• Inconsistent naming of sections across different tutorials, there should be some standardized way
  • If we use digits we should use it everythere.
  • We should use the same title hierarchy.
• Inconsistent placing of imports. We should place imports the same way in each tutorial.
  • I'm not sure is that necessary or not.
• Inconsistent metion of extras necessary to install. It should be at the very top of the tutorial for each of them.

Add created specification for styling of notebooks into contribution guide.

Test cases

No response

Additional context

Developing in docs-prototype branch.

[Mr-Geekman]

Closed by #1330.